HOW TO GROW RHODODENDRONS THAT THRIVE

Rhododendrons come in all shapes, colors and sizes. Growing this fascinating group of plants is easier than many think. Importantly, there is a lot of mis-information out there. I see people preparing soil where none is needed or preparing it incorrectly. Often doing less preparation is the right thing if your soil is right. READ ON

We are located in zone 5b officially but last winter felt like zone 1. We went to 18 below zero, the coldest I have ever seen here. Though we are 2 miles from the ocean here in Maine, the waters moderating effect is not that great, as the water is south of land, and the cold winds blow from the north/northwest.

If you live in the following states at least some rhodos can be grown where you are. In more southern states listed, azaleas are easier than rhodos. (azaleas are rhodos)

As someone who has grown rhododendrons from the age of 16, in both NJ and Maine, very successfully, and by the thousands, I can speak with some confidence on this topic. I do like to be challenged, so if you disagree please comment. Some of these comments might seem out of the main stream, so be it …but they are fact.

OUR WOODLANDS ARE FULL OF BLOOMING BEAUTIES

There are literally thousands of rhodo hybrids and species. In any one climate, perhaps only a fraction of those can be grown but in general, they will thrive from the mid Atlantic to New England to the upper midwest …depending on the cultivar, hybrid or species. (and the Oregon/Wash coast is rhodo heaven …but those of us in the east have many ideal areas also!)

WHAT TYPE OF SOIL? This is where I see lots of bad info!!! Rhodos evolved in both woodland, forested climates and more open, mountain climates. Mimicking what nature did is always best but even better is not trying to mimic it, but just “having the right conditions and soil naturally” …and many areas do. They can grow well in woodland soil with organic matter and mountain type soil that is gravelly also.

WATER LOGGED SOIL A NO NO

Here at the nursery our soil ranges from pure sand to soil with a peaty* layer on top with sandy soil below to very peaty/organic to heavier soil. In many cases the soil is shallow and only 3-5 inches deep before hitting ledge and rock & that’s fine, for rhodos. That peaty layer is usually the result of a hundred years of rotting oak leaves and various mosses. Rhodos love it. Naturally peaty soil if fine, but making it and amending stuff to make it, is not as good or easy.

If you have good draining woodland soil DON’T TRY TO IMPROVE IT. At our nursery we have ideal woodland soil; it varies but generally we don’t do anything when planting except add Soil Moist or Terra Sorb to the planting area. Generally speaking, if you you have oaks, that’s a good sign your soil is fine as is. Come visit, you will see the best looking rhodos anywhere on the east coast …and again, we do nothing to improve the soil.

SOIL MOIST AND TERRA SORB These are water retaining crystals that after expanded with water, are added to the edges of the rhodo root ball and under it when planting. We use them here and they work amazingly well. They give the plants an edge in that it reduces chance of drought stress and generally gives better growth. They must be fully expanded in water before using. Most garden centers have it. Email if you have questions.

ONE OF OUR OWN EXCLUSIVE HYBRIDS RASBERRY SPLASH

PLANT SHALLOW AND DON’T COMPRESS SOIL HARD Rhodo roots are shallow and fine textured. When planting plant at same level as root ball, not deeper. Firm soil around edges but NEVER STEP ON SOIL to compact it. Also, make sure the root ball is wet or damp before planting. After planting, water the plants in, but not to the point of flooding. They can’t take overly wet soils (with a few exceptions)

IF YOU HAVE UP AND DOWN LAND ON A SLOPE This is often ideal as it drains well, so if your land has contours, use them, don’t flatten them. In nature rhodos are often found on sloped areas.

SITE OUT OF WIND Generally speaking sites out of windy locations are always best, yet I can say my property is windy and when you see how they are thriving!

HEAT AND COLD-BOTH ARE FACTORS People often think it’s just the cold that can hurt plants but heat can be just as bad. Rhodos generally do better in the cooler-colder states or at least states that don’t have long, hot summers …so that rules out the deep south in general for rhodo growing but there are a few exceptions. Here in Maine on the coast we can grow as many (but sometimes different) rhodos as the mid Atlantic area due to cool summers.

RHODOS FOR COLD AREAS & RHODOS FOR HOT AREAS Some are better adapted for hot or cold areas, if in doubt just ask us

SUN OR SHADE Rhododendrons are often called shade plants but that’s not entirely true. Some want full sun, especially smaller leaved types. Sun from dawn to noon is fine. If you look up and see patches of sky AND patches of leaves that’s generally good …giving you filtered shade. Generally speaking, in areas up north they can take more sun (but beware of scorching winter sun in next paragraph) In milder coastal locations they can take more sun also.

IN FAR NORTHERN CLIMATES WINTER SHADE HELPS When the ground is frozen in the north, bright winter sun can dry the plants out as they cannot take up moisture when the ground is frozen. Siting your rhodos so they get some shade in winter will help. Winter shade can come from trees especially evergreen trees whose branches shade when the sun angle is lower in winter. Shade can even come from cut evergreen boughs stuck in the ground in late fall to provide a bit of shade. NEVER BURLAP rhodos to protect them. If you must do this, erect a burlap screen a foot or two away from plant toward the windy side …that will help if they are in a very windy area.

ONE OF COUNTLESS WOODLAND SCENES DURING BLOOM AT THE NURSERY

DON’T ADD TOO MUCH ORGANIC MATTER Oh this irks me …I hear people say “I added lots of peat moss and compost” to the rhodo area …well, that will generally kill them over time as the organic matter breaks down into muck. If your soil is clay and sticky you must add sand and gravel and some organic matter. Rhodos need organic matter but it should not be over done. If you have NATURALLY organicy soil from rotting pine needles or fir or hemlock and oak leaves that is perfect.

SAND AND GRAVEL if you have heavier soil add sand and gravel not just peat moss

MAN MADE COMPOST IS A NO NO I can hear the screams….what is this man saying? Compost from anything except oak leaves is bad. It has the wrong texture and often ph and is full of earthworms! Adding crushed/ground oak leaves to soil is good.

EARTHWORMS ARE AN ENEMY OF RHODOS I can see you shaking your head. EARTHWORMS MAKE THE SOIL TOO CRUMBLY FOR RHODO ROOTS and they raise ph. The crumbly black dirt earthworms make is not good for them. If you grow rhodos, pluck out earthworms when you see them, Rhodos want friable soil yes yes..but not the type earthworms make. earthworms no, compost no. Next time you are in an oak forest, pick up the first few inches of dirt and leaf litter….that’s the type of soil rhodos want. Its layered and spongy but not pebbly and crumbly.

ROOT BOUND AND POT GROWN RHODOS …TRY TO AVOID THEM We grow our rhodos in the ground or shallow flats, which mimics the natural shallow root systems they have …no other nursery we know of does that. It is much healthier for the plant and prevents them from being root bound. If you do purchase root bound rhodos, the outer roots must be loosened before planting.

A BEAUTY FROM OUR BREEDING PROGRAM, NOT AVAILABLE QUITE YET

MULCH WITH OAK LEAVES …PINE NEEDLES ARE GOOD TOO GGRRGGG what to mulch with. If you have them, by far the best mulch is oak leaves. Nothing else comes close. If you have oak tress or people in your area rake away the oak leaves..gather them up and use them as mulch. Almost all plants will benefit. PINE NEEDLES make a good mulch too and we use them here. Excess mulch will kill rhodos over time. I see this happen all the time. Think about it. Does a rhodo growing in the woods naturally get 5 inches of wood chips poured on top of it every year? …of course not. Over mulching is one of the biggest scams in horticulture …its a way for “landscapers” to make money, that’s all. If you are growing your rhodos in a natural woodland environment, after a year or two …the falling leaves in fall may be all they need. We dont like using bark or nuggets but if you must they must be from softwood (evergreen) trees.

DO NOT MULCH WITH HARDWOOD CHIPS UNDER ANY CIRCUMSTANCE I will talk about that in a future blog post. So, oak leaves are the best but oak (and maple, etc) chips are a no no.

KILLING THEM WITH KINDNESS …PLEASE DON’T TREAD ON ME Due to the fine delicate roots of rhodos we actually can kill them with kindness so do not walk on the root area of rhodos, generally the width of its branches. This is one of the most important things to remember. Those roots grow slowly, stepping on the root ball can literally rip off parts of the root system.

NEVER RAKE HARD UNDER RHODOS Rhodo roots are shallow, raking hard under them can literally rip the roots away. Leave the leaves that fall there, they are a natural mulch.

FERTILIZER We do fertilize here both with dry and water soluable fertilizers. A general fertilizer with nitrogen in urea form is good; do not use nitrate based fertilizers (see label for what nitrogen is from) Mira Acid does work well as do other water soluable fertilizers. Generally, do not fertilize after late July. We fertilize starting in May thru late July. For the average homeowner a few feedings in spring is fine. Read the label.

WATERING Don’t let them go totally dry, even once it will kill them when they are young. After they are established in the ground it is a different story but newly planted rhodos, at least the first year must not be allowed to go bone dry. Always water the transition zone where root ball stopped and loose soil began.

COVERED IN FLOWER BUDS Did you buy a rhodo covered in flowers buds on every branch..that’s not a good thing. All those flower buds are produced by excess fertilizer and in some cases growth hormones which do the plant no good. If you bought a 3 foot rhodo with buds everywhere carefully break off half. It takes somevcourage but you will do the plant a word of good, and save its strength for better growth and ultimately a better plant.

HARDINESS RATINGS I see rhodos sold in many places that are not the least bit hardy, very sad. If in doubt feel free to email us. At Eastern Plant we test all rhodos for hardiness …like no one else. YOU CAN TRUST OUR HARDINESS RATINGS. We specialize in superior, hardy varieties that you cannot get elsewhere. Thirty years in business shows that …we have stood the test of time.

ALL our rhodos are grown in the tough climate of the northeast and over winter OUTSIDE …IT MAKES A HUGE DIFFERENCE.

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1 thought on “HOW TO GROW RHODODENDRONS THAT THRIVE”

This is a great overview and very good details on how to take care of and plant rhododendrons. Thank you very much Mark. I’ve really learned a lot reading this. It’s great! I’m sure I’ll be using this for a resource now and in the future. I hope you have a great weekend! Thank you again for sharing your love and expertise for rhododendrons!!